In the automobile industry and the machinery industry, etc., there has been increased demand for sensors capable of precisely detecting a physical quantity such as acceleration or angular velocity. Particularly, small sensors capable of detecting these physical quantities for two-dimensional or three-dimensional components are demanded.
As such small sensors, a novel sensor which has been developed by the same inventor as that of the present application has been disclosed in the Japanese Patent Application Laid Open No. 5-26744/1993 publication. In this novel sensor, plural sets of detection elements comprised of a piezoelectric element are prepared and these sets of detection elements are disposed on a flexible substrate. This novel sensor is of a structure in which a working body is attached on the flexible substrate so that when external force is applied to the working body, bending takes place in the flexible substrate. This bending is transmitted to the piezoelectric element, and charges corresponding to the bending are produced in the piezoelectric element. Thus, the applied external force is detected on the basis of such charges produced. This is the fundamental principle of the novel sensor. Since a way of bending changes in dependency upon the direction of the applied external force, an approach is Employed to detect the state of charges produced with respect to plural piezoelectric elements disposed at predetermined respective positions, thereby making it possible to detect magnitude and direction of the applied force. Moreover, in the Japanese Patent Laid Open Application No. 7-43226/1995 publication, a technology for permitting similar detection by a lesser number of detection elements is disclosed.
On the other hand, in the International Laid Open No. W094/23272 publication based on the Patent Cooperation Treaty, there is disclosed an angular sensor in which plural piezoelectric elements are similarly disposed on a flexible substrate to thereby detect angular velocity components about respective three-dimensional axes. This angular velocity sensor utilizes the principle that when an object is oscillated in the Y-axis direction in the state where angular velocity .omega.x about the X-axis is applied, Coriolis force is exerted in the Z-axis direction. Namely, an a.c. voltage is applied to a predetermined piezoelectric element disposed on the flexible substrate to oscillate the working body attached on the flexible substrate in the Y-axis direction. In this case, since when angular velocity .omega.x about the X-axis is applied, a Coriolis force is exerted on the working body in the Z-axis direction, the working body is caused to undergo displacement in the Z-axis direction. This displacement is detected by charges that the piezoelectric element produces to thereby indirectly detect the applied angular velocity .omega.x.
In the case where acceleration components or angular velocity components with respect to three-dimensional directions are detected by a single sensor, the technologies which have been proposed until now are required to dispose a large number of electrodes at predetermined positions, resulting in the problem that the structure becomes complicated as a whole. In sensors of such complicated structure, there takes place the problem that miniaturization becomes difficult, so mass-productivity is poor.